1. Field of Invention
The present invention relates to a battery voltage regulating system for controlling an output voltage of an alternating current generator driven by an internal combustion engine and/or a charging voltage for a battery mounted on a motor vehicle.
2. Brief Description of Prior Arts
Various types of battery voltage regulating systems are known in the art, wherein either a battery voltage or an alternator output voltage is sensed and a field current flowing through a field coil of an alternator is cut off when the sensed voltage exceeds a predetermined value, to thereby maintain the battery voltage at a constant desired value.
In a conventional battery voltage regulating system, for example, disclosed in U.S. Pat. No. 4,346,338, when a feedback voltage (an output voltage of an alternator) exceeds a reference voltage, a field current is immediately cut off while when the feedback voltage becomes lower than the reference voltage, the field current is immediately supplied to a field coil. In such a conventional system, an ON-OFF frequency of the field current largely changes depending on a rotational speed of the alternator, an amount of load current and so on, with a result that the battery voltage may overshoot a desired value to a large extent.
In another conventional battery voltage regulating system disclosed in Japanese Unexamined Patent Publication No. 55-18839, a switching element for controlling a field current is forcibly made on and off irrespectively whether a feedback voltage is higher or lower than a reference voltage, and an ON-OFF frequency of the switching element is instead controlled depending on a difference value between the feedback voltage and the reference voltage, so that the battery voltage is effectively prevented from overshooting a desired voltage.
It has, however, still a disadvantage in that the battery voltage is changed in response to a change of the ON-OFF frequency of the switching element, since when it is required to increase or decrease the ON-OFF frequency, the difference value between the feedback voltage and the reference voltage should become correspondingly smaller or larger, which means that the battery voltage should be changed in order to change the ON-OFF frequency.